Electric heating switch



June 3, 1952 H. F. FREEMAN 7 ELECTRIC HEATING SWITCH Filed June 24, 1949 '7 Sheets-Sheet 2 A3 Mb FIG. 3

INVENTR June 3, 1952 H. F. FREEMAN 2,599,171

ELECTRIC HEATING SWITCH Filed June 24, 1949 '7 Sheets-Sheet 3 FIG.- 5

FIG.- 6

June 3, 1952 H. F. FREEMAN 2,599,171

ELECTRIC HEATING SWITCH Filed June 24, 1949 '7 Sheets-Sheet 4 0 0 '"3 qo\ 9 Bla Q 95 IOI 10 9 97 I00 X g 9!. 93 7 '05 CH INVENTOR June 3, 1952 FREEMAN 2,599,171

ELECTRIC HEATING SWITCH Filed June 24, 1949 7 Sheets-Sheet 5 j i ///z FIG.- IO

FlG.- ll

INVENTOR June 3, 1952 H. F. FREEMAN ELECTRIC HEATING SWITCH 7 Sheets-Sheet 6 Filed June 24, 1949 w n J Eta @El H H 3 w.

5 a 8 b 2 n n FIG.- l2

#122. In G\ INVENTOR O 2 I W l 9 I H r- Hm? I R \4 Q G F 2, 2 I 2 H Patented June 3, 1952 UNITED PATENT F FICE ELECTRIC HEATING SWITCH- Hadley'FL' Fieeman; Pittsburgh; Pai, assignor tu Edwin Wiegand' Company;-Pittsburgh,- Pa., acorp'orationof Pennsylv'ania ApplicaticniJimell', 1949,.Serial'N6. 101,200"

My switch, and the principal object ofmyinven tion is to provide improvedmeansfor controlling the energization of oneor more electric heaters:

One applicationfor which my invention is particularly suitable is. to control? one or? more top units of an electric range orhot'plate, for example, all four of the topunits'ofacustomary four-top-unit electric range; andI have herein illustrated my invention inttliis utilization:

Therefore in the drawings accompanying'this specification and forminga partof this application I have shown for purposes of" illustration what Inow consider to'be the bestmodes'of carrying my invention into practicelin" this':par= ticular utilization, and in these drawings:

Figures 1 through 4 are diagrammatic: rep resentations of' four circuit arrangements for that purpose;

Figure is an elevationof'onei formcfswitch mechanism suitable. for. eitherthe arrangement of Figure 1 or the arrangement of Figurer3 3.

Figure 6 is an elevation of one form of switch mechanism suitable for either the: arrangement of Figure 2 orthe arrangement'fof Figure"4;

Figure Iis a general 'view'of the'swi'tchmeans of either the mechanism of Figure- 5 or the mechanism of Figure 6;

Figures 8' and 9" are" views indicating other positions of the switch means ofFigure 7;

Figure 10is an elevationrofia'second form of switch mechanism suitable. for either the ar-" rangementof Figure l'ior the arrangementof Figure 3;

Figure 11 is an elevation oifasecond form of switch mechanism suitable for. either. the. arrangement of Figure 2 or the arrangement of Figure 4;

Figure 12 is a general .viwof Ltheswitch means of either the mechanism offFi'gure. 1'0.-or. the mechanism of Figure 11;.v

Figures 13 and 14 are views-indicating.other positions of the switchmeans of ZFigure 12.

Figure 15 is a view showingla supplemental cam desirab1e in..-the utilization of eitherof the above switch. means .ineither the. arrangement of Figure 1 or the arrangement ofFigure' 3E and Figures 16 through 18 L- are. views indicating three positions oflthe abovesupplem'entalcam and of the supplemental switch means'controll'ed. thereby.

In Figuresv l and 2.1 have illustrated'itwo methods of utilization in" conjunctiomwith four top units 2! each comprising two heating'ele= invention relates to electric. heating.

2 ments or races 22 and 23 each designed to be energized'at the same'voltage, and according to eitherofthese arrangements the two races of each unit are operatively'connected in parallel, as'indicated' by the conductors 24 and 25;

In the arrangement represented in Figure 1', current is supplied by two supply conductors 26 and 27 towhich is connected a synchronous electric" clock 28, and each of the units 2| is connected to the supply conductors26 and 2'! respectively'by. a branch" conductor 29 in which is interposed a' control switch 30 and a branch conductor'tl in which may be interposed a supplemental'switch 32:

In thearrangemen't' represented in Figure 2, current" is'supplied'fr'om a three-wire feed consisting'of potentialconductors 33 and 34 and a neutral conductor 35; through a three-polerea'dy switch't36', to potential conductors 31 and 38' and a neutral conductor 39', and connected to the potentialconductortl and the neutral conductor 39 is a synchronous motor 40, connected to the potentialconductor 38 and the neutral conductor 3'9-is a tell-tale lam'p 41; each of'the units 2i is connected to the potential conductors 31 and 38 by. branch conductors 42 and 43, andin each branch" conductor 42 is' interposed a control switch 44.

With the-foregoing, if a switch 32" of a unit 2| of Figure l' is in closed position and the switch 3110f thatunit'isclosed; or if the switch 44 of aunit 2'! of Figure 2is closed, the two elements 22and'2'3 of'that'unit will each be connected to rated' voltage, and the. unit will be fully energized and. willdeliver full rated heat, whereas if the switch Sit-or 44 is-open, both races of the respective unit' will be disconnected; notenergized} and will deliver no heat.v

on the other. hand, ifthe switch 3 2 of a unit 2| of Figure-11s in closed position and the switch 3o-of that unit .is cycled between open and closed positionsby; means of the clock 28; or if the switch 44 of a unit 2] of Figure 2 is cycled betweenopenand closed. positions by means of the motQrAO th'ereupOn that unit will be energized and will deliver-that'proportion of its rated heat dependent-upon and'directlyproportional to the proportion of eachcy'cle during which the switch 30 or 441.5. inclosed position Optionally the arrangementpf Figure 1 may include atneutral conductor, andin" that event the clock 28 may be I connected to: this neutral conductor'and: one of the conductors 26an'd '21, inanyf'event the arrangement ofFigure 1 may include *atelI-ta1e"'lamp' "sirnilanto' the lamp 4 l of Figure 2 and connected either to the two conductors 26 and 21 or to one of these and the indicated neutral conductor, and on the other hand, in the arrangement of Figure 2 the ready switch 36 may be only two-pole, omitting the neutral, and either the neutral conductor 39 may be connected directly to the neutral conductor 35 or the neutral conductors 35 and 39 may be omitted entirely and the motor 40 and lamp 4| connected to the two potential conductors 31 and 33, also the lamp 4| may be omitted entirely.

In Figures 3 and 4 I have illustrated two methods of utilization in conjunction with four top units each comprising an element or race 52 designed to be energized at a higher voltage and an element or race 53 designed to be energized at a lower voltage, for example, one half of the higher voltage, and according to either of these arrangements the races 52 and 53 of each unit 51 are connected together on one side, as indicated to the potential conductor 55, respectively by branch conductors 59a and 59d, the one side of the elements or races 52 and 53 of each of the units 5Ib and 5Ic is connected to the potential conductor 56, respectively by branch conductors 59b and 590, and interposed in each of the branch conductors 59 is a control switch 60.

The other side of the high voltage element or race 52 of each of the units 510. and 5111 is connected to the potential conductor 56, respectively by branch conductors 61a and 61d, the other side of the high voltage element or race 52 of each of the units 511) and 5lc is connected to the potential conductor 55, respectively by branch conductors 61b and 610, the other side of the low voltage element or race 53 of each of the units 5| is connected to the neutral conductor 57, by a branch conductor 62, and optionally interposed in each of the conductors 6| is a supplemental switch 63.

In the arrangement indicated in Figure 4, current is supplied from a three-wire feed consisting of potential conductors 64 and 65 and a neutral conductor 66, through a three-pole ready switch 61, to potential conductors 68 and 69 and a neutral conductor 10, and connected to the potential conductor 68 and the neutral conductor is a synchronous motor 1|, and connected to the potential conductor 69 and the neutral conductor 10 is a tell-tale lamp 12.

The one side of the elements or races 52 and 53 of each of the units 51a and 51d is connected to the potential conductor 68, respectively by branch conductors 13a and 13d, the one side of the elements or races 52 and 53 of each of the units 51?) and 5lc is connected to the potential conductor 69, respectively by branch conductors 13b and 130, and interposed in each of the branch conductors 13 is a control switch 14.

The other side of the high voltage element or race 52 of each of the units 5la and 5161 is connected to the potential conductor 69, respectively by branch conductors a and 15d, the other side of the high voltage element or race 52 of each of the units 5lb and 510 is connected to the potential conductor 68, respectively by 4 branch conductors 15b and 150, and the other side of each of the low voltage elements or races 53 is connected to the neutral conductor 10, by a branch conductor 16.

With the foregoing, if a switch 63 of a unit of Figure 3 is in closed position and the switch 60 of that unit is also closed, or if the switch 14 of a unit of Figure 4 is closed, the two elements or races 52 and 53 of the respective unit will be connected each to its rated voltage, and the unit will be fully energized and will deliver full rated heat, whereas if the switch 60 or 14 is opened, the two elements or races of the respective unit will be connected in series to th rated voltage of the element or race 53 and the unit will be only fractionally energized and will deliver only a fraction of its rated heat, the fraction depending on the relative resistances of the two elements or races 52 and 53.

On the other hand, if the switch 63 of a unit of Figure 3 is in closed position and the switch 60 of that unit is cycled between open and closed positions by means of the clock 58, or if the switch 14 of a unit of Figure 4 is cycled between open and closed positions by means of the motor H, thereupon that unit will be energized and will deliver that proportion of its rated heat, within the range from the fractional amount of the series connection to full rated capacity, dependent upon and determined directly by the proportion of each cycle during which the switch 60 or 14 is in closed position.

As an example, if the two elements or races are of equal wattage, for which the resistance of the element or race 53 would be one-fourth the resistance of the element or race 52, thereupon the fractional energization in the series relation would be one-tenth, in the series relation the unit would deliver one-tenth its rated heat, and under the cycling operation of the switch 60 or 14 the heat delivered by the unit would be variable from 10% to of the full rated heat of the unit.

In this respect, normally there is no occasion to operate a top unit of an electric range or hot plate below 10%, also normally there is no occasion to operate such a unit below 100% and at more than approximately 60 to 75%.

Optionally the arrangement of Figure 3 may include a tell-tale lamp similar to the lamp 12 of Figure 4 and connected to the two potential conductors 55 and 56 or to one of these and the neutral conductor 51, in the arrangement of Figure 3 the clock 58 may be connected to the neutral conductor 51 and one of the potential conductors 55 and 56, and in the arrangement of Figure 4 the ready switch 61 may be only two pole, omitting the neutral, and the neutral conductor 10 connected directly to the neutral conductor 66, either or both of the motor H and lamp 12 may be connected to the two potential conductors 68 and 69, and also the lamp '12 may be omitted entirely.

Furthre, if any of the units 21 or 5| are of the sheathed type, the two elements or races 22 and 23 or 52 and 53 of each unit may be in separate sheaths, or may be included in a single sheath.

In any of the arrangements of Figures 1 through 4, the control switches 30, 44, 60, or 14, may be provided by the switches 8| of the switch mechanisms 82 and 83 shown in Figures 5 through 9, or by the switches I ll of the switch mechanisms H2 and H3 shown in Figures 10 through 14.

As shown in Figures. andi. each. of the switch mechanisms 82; and. 93 comprises; four control knobs or handles, 8.4, the switch mechanism 82 comprises on its. front; a, clockv 85: suitable to constitute the clock. 28 or: 58 of'the. arrangements of Figures, 1 andl3; and therefore is intended particularly for utilization, with the arrangements of Figures 1 and 3,- and theswitch mechanism 83 compriseson its rear a. synchronous motor 85 suitable to constitute the motor Iill or 'II of the arrangements. of; Figures 2 and 4, and on its front a, lamp 8;! suitable toconstitute the lamp 4| or I2 of the, arrangements of Figures 2 and 4, and therefore intended particularly for utilization with the arrangements of Figures 2 and 4.

As shown in Figure 7, each of they switches 9| comprises an actuated electrically-conducting resilient arm 83 and a cooperating electricallyconducting resilient arm 89; andthearms 8,8 and 99 are provided at theirouter ends withintegral lateral extensions 99 by which the arms are riveted or otherwise suitably mounted to. a common electrically-insulating base 9:], andare provided at their inner endswith cooperating contacts92 located to be brought into engagement upon suitable actuation of the actuated arms 88,, thus to close the respective switch M.

For this purpose thefour switchssBI, are. disposed about a common cam 93, fixed to and rotatable by a shaft 94 operated either by the .clock 95 of the mechanism of Figure 5 or by the motor 99 of the mechanismofFigure 6, and constructed and arranged upon such rotation tocyclically sequentially actuate theactuatedarms 8,9 and bring the contacts 92into engagement, but under the control of individual switch control means 95.

In the present embodiment, each of. the control means 95 comprises a shaft, 96, constructed to receive and be operated by the, respective cone trol knob or handle 84; and providedwith two cams, an actuated-arm control cam 91 located to act upon a coacting follower surfaceSB unitary with the respectiveactuated arm. 88 and thereby to determine the primary'position of the respective actuated arm 88', and;a;cooperatingarm control cam 99; locatedto act upon a coacting follower surface I99 unitary with the respective cooperating arm;.89-. and thereby. todetermine the primary position of the respective cooperating arm 89.v

As herein shown, each of the actuated-arm control cams 91 comprisesa substantially, concentric portion I9I subtending what will :be re,- ferred to as the variablerange, anda projecting portion I92 subtending what willbe referred to as the off and on positions, and each of the cooperating-arm control cams. 99 comprises an off projection I93, a higher on projection I94, and a variable range portion I95 rising continually from adjacent the on projection I94, to adjacent the off projection I0 3,; but thehigh end of which is substantially below the-elevation of the off projection I03.

In the position in which the parts areshown in Figure 7, each of the control meansi95cis set for cycling operation, and for. maximum period of closure of the contacts 92. during eachcycle. of the actuating cam 93. However, inthe. present embodiment, as indicated by the positionsof the arms 89 and 99 of the switches 81a andBIb', even in this adj ustment the cooperating-arm control cams 99 hold the cooperating arms-99 at such elevation that the contacts92-are open'during a substantial portion ofeach cycleof the actuating cam 93, as herein shown, approximatelyi20%: of each cycle.

Further, by reason of. the contour of the co.- operating-arm control cam 99, upon rotation of a control means 95, in the clockwise-direction as viewed in Figure 7, the respective operating arm 89is progressively raised, whereby progressively the contacts 92. are closed only. during. a correspondingly decreased portion of eachcycle; until atthe end' of thevariablerange portion I95the contacts 92 remain open throughout. substantially the entirety of each cycle.

Therefore each of the control. means 95: is eifective to vary theportion-of each cycle during which the contacts.92 of. the respective switch 8i areclosed, to causethercontacts-92 to beiclosed during any desiredproportion'.of'the cycle from a maximum substantiallyless than 109 as herein shown, approximately to andincluding substantially zero.

Thus. in conjunction with. the actuating cam 93, each control means is effective over thevariablerange to cause a. respectiveunit 2 I, to gen.- erate any proportion of. full ratedheat. between a maximum substantially less than as herein shown, approximately 80%, and a. minimum substantially zero, or to cause. a respective. unit 5| to generate any proportion of full rated heat between a maximum substantiallyv less than 100%, as herein shown, the sum of approximately 80% plus the product. of approximately 20% multiplied by'the fraction of full heat generated in the series relation, and a. minimum substantially that fraction, or under. thev previous example of that fraction as. oneetenth, as herein shown, between a; maximum of approximately 82% and a minimum of approximately 10%.

As indicated in Figure. 8, upon further rotation of the control means 95, the actuated-arm control camill raises theactuated arm 88. entirely outof the path'ofthe actuating cam 93, but the cooperating-arm control cam 99 raises the cooperating arm 89v still further, resultingin the contacts 92 being maintained separated, and thereby providing afull off condition.

As indicated in Figure. 9; upon still further rotationof the control means 95, the actuated-arm control cam 91 still holds the actuatedarm 88 out ofthe path of the actuating cam 93, but the cooperating-arm control cam- 99raises thecooperating arm- 89. still. higher, thereby bringing a fu-rther contact I06 carried on the. reverse side of the arm 99, into engagement with astationary contact I91 mounted on an L-shape electricallyconducting post I99 riveted or otherwise suitably mounted to the base 9| and electricallyconnected to the actuated arm 88 as by aconductor I98, and thereby providing a full on? position.

Further rotation of a control means 95' from the above full on position resultsv in again bringing the parts into the variable range portion perviously described. However, in the present embodiment the controlmeans-95are rotatable in either direction.

As shown in Figures 10 and 11, eachof the switch mechanisms H2 and I [loomprises four control knobs or handles H4,- the switchmechanism II2 comprises on its front a clock IIE-suitable to constitute the clock 28 or 58.:of the arrangements of Figures 1 and 3, and therefore is intended primarily for-utilization with-the arrangements of Figures 1 and 3, and-the switch mechanism I I3 comprises at one side a motor I I6 suitable to constitute the--motor= Kor -lot the arrangements of Figures 2 and 4, and on its front a lamp II'I suitable to constitute the lamp II or T2 of the arrangements of Figures 2 and 4, and therefore is intended particularly for utilization with the arrangements of Figures 2 and 4.

As shown in Figure 12, each of the switches II I comprises an actuated electrically-conducting resilient arm H8 and a cooperating electricallyconducting resilient arm II9, and the arms H8 and H9 are provided at their outer ends with integral lateral extensions I20 by which the arms are riveted or otherwise suitably mounted to a common electrically-insulating base I2I, and are provided at their inner ends with cooperating contacts I22 located to be brought into engagement upon suitable actuation of the actuated arm H8, thus to close the respective switch III.

For this purpose the four switches III are disposed in parallel relation and arranged to be actuated respectively by a series of four cams I23 fixed to and rotatable by a shaft I24 operated either by the clock II of the mechanism of Figure or by the motor II6 of the mechanism of Figure 11 and constructed and arranged upon such rotation to cyclically sequentially actuate the actuated arms I I8 and bring the contacts I22 into engagement, but under the control of individual switch control means I25.

In the present embodiment, each of the control means I25 comprises a shaft I26 constructed to receive and be operated by the respective control knob or handle H4 and provided with two cams, an actuated-arm control cam I21 located to act upon a coacting follower surface I28 unitary with the respective actuated arm H8 and thereby to determine the primary position of the respective actuated arm I I8, and a cooperating-arm control cam I29 located to act upon a coacting follower surface I30 unitary with the respective cooperating arm I I9 and thereby to determine the primary position of the respective cooperating arm I I9.

As herein shown, each of the actuated-arm control cams I2! comprises a substantially concentric portion I3I subtending what will be referred to as the variable range, and a projecting portion I32 subtending what will be referred to as the off and on positions, and each of the cooperating-arm control cams I29 comprises an off projection I33, and lower on projection I I34, and a variable range portion I35 rising from adjacent the on projection I34 to adjacent the off projection I33, but the high end of which is substantially below the elevation of the on projection I34.

In the position in which the parts are shown in Figure 12, each of the control means I25 is set for cycling operation, and for maximum period of closure of the contacts I22 during each cycle of the actuating cams I23, and as indicated by the positions of the arms H8 and H9 of the various switches III, in the present embodiment in this position of the control means I25 the contacts I22 are in engagement during substantially the entirety of each cycle.

However, by reason of the contour of the cooperating-arm control cam I29, upon rotation of a control means I25, in the clockwise direction as viewed in Figure I2, the respective cooperating arm H9 is progressively raised, whereby progressively the contacts I22 are closed only during a corresponding decreased portion of each cycle, until at the end of the variable range portion I35 the contacts I22 remain open throughout substantially the entirety of each cycle.

Therefore each of the control means I25 i effective to vary the portion of each cycle during which the contacts I22 of the respective switch III are closed, to cause the contacts I22 to be closed during any desired proportion of the cycle, from a maximum substantially to a minimum substantially zero.

Thus in conjunction with the actuating cams I23, each control means I25 is effective over the variable range to cause a respective unit 2I to generate any proportion of full rated heat between a maximum substantially 100% and a minimum substantially zero, or to cause a respective unit 5| to generate any proportion of full rated heat between a maximum substantially 100%, and a minimum substantially the fraction of full heat generated in the series relation, under the previous assumption, approximately 10%.

As indicated in Figure 13, upon further rotation of the control means I25 the actuated-arm control cam I2'I raises the actuated arm II8 entirely out of the path of the respective actuating cam I23, but the cooperating-arm control cam I29 raises the cooperating arm H9 still further, whereby the contacts I22 are maintained separated, thereby providing a full off position, and as indicated in Figure 14, upon still further rotation of the control means I25, the actuated-arm control cam I2'I still holds the actuated arm II8 out of the path of the respective actuating cam I23, but the cooperating-arm control cam I29 permits the cooperating arm I I9 to drop to bring the contacts I22 into engagement, thereby providing a full on position.

Further rotation of a control means I25 from the above full on position results in again bringing the parts into the variable range previously described. However, in the present embodiment the control means I25 are rotatable in either direction.

With any of the mechanisms of Figures 5 through 14, the period of each cycle desirably should be sufficiently short to avoid objectionable variation in temperature of the heating unit under the cycling operation, and on the other hand, for the purpose of avoiding unnecessary wear and fatigue of the parts, should not be shorter than is necessary, and under these considerations, in the event of sheathed units the duration suitably may be of the order of from 60 to seconds, depending partly upon the thermal lag exhibited by the particular construction of heating unit employed, and in any event being permissibly somewhat longer than the arrangements of Figures 3 and 4, by reason of the energization not being entirely interrupted.

As herein shown, in the switch means of Figures 5 through 9 the switches 8| are substantially equally spaced about the actuating cam 93, and in the switch means of Figures 10 through 14 the actuating cams I23 are substantially equally spaced angularly about the axis of the shaft I24, thus tending to even the power demand when more than one of the units 2I or 5| are concurrently energized under cycling operation.

In either of the switch means herein illustrated, preferably the contour of each actuatin cam 93 or I23 is substantially uniformly accelerating over approximately the first half of its periphery and then substantially uniformly decelerating over approximately the second half of its periphery, thus tending to smooth the action of the cams on the respecting actuated arm 88 or I I8, except only for the movement at the step of the cam.

On the other hand, the inclusion of the step,

on separation of the contacts under load, and

'thu'sto increase the life of i the contacts.

Further, raising the actuated-arms 88 or H8 out of ngageme with the actuated cam 93 or cams 123 in both the"full off and full on positions, results in eliminating unnecessary wear of the'cam or cams 93 or I23 and or the actuated arms 8? or Hi8, and unnecessary fatigue of the actuating arms 88 or H 8 and of the cooperating "arms 85 or I f9.

This "is particularly important in the arrangeitems of Figures 1 and 3, which as herein s 'h own'tlie cam er cams 93 or 123 operate continuously, as distinguished from "the situationin the arrangements of Figures 2 and 4, in which properly the ready switch 36 or 61 is closed only preparatory to utilization of any of the units 2| or 51-, andjis opened upon'cessation of utilization "of any of the units, whereby the respective motor is connected, and the cam or cams 93 or I23 are in operation, only duringperiods of actual utili- "zation 'of one or more of the units 2| or 5|.

In the arrangements of Figures 2 and 4, inasmuch as the units 2! or 5| also are connected on the load side of the ready switch '35 or 6?, there'idre the ready switch 36 or 61 serves also to 1 completely disconnect the units 21 or '5I at least from "the potential -'conductors, "and thus to meet a requirement to that effect prevailin in many localities.

For this reason a suitable ready switch may be 1 included also in the arrangements of Figures 1 and 3, or these arrangements maycomprise the individual switches 32 and 63 heretofore referred to, and in that event these switches 32 and 53 may be arranged to be opened automatically upon contact post I4I carrying a contact I42 and comprising an integral lateral extension I43 by which the post is riveted or otherwise suitably mounted to the base 85 or II5, a further electricallyconducting resilient arm I44 carrying a cooperatin contact and comprising an integral lateral extension I45 by which the arm I44 may be riveted or otherwise suitably mounted to the base or I I5, and on the shaft of each control means as or I25, a further cam I41 provided with a single projection I48 registered to engage the arm I44 and separate the contacts I42 and I45 when the respective control means or I25 is in the full oil position, as indicated in Figure 16, but to permit the contacts I42 and I45 to be in engagement both in the full on position, as indicated in Figure 17, and over the variable range, as indicated in Figure 18.

Obviously the above supplemental switch may be included also in the arrangements of Figures 2 and 4, also optionally the control means 95 of Figures 5 through 9 may be modified to not limit to substantially less than the maximum proportion of the cycle during which the contacts 92 or 22 are closed, the control means I25 of Figures 10 through 1 may .be modified to limit to substantially less than 100% the maximum proportion of the cycle during which the contacts 92 or I22 are closed, and either the control means 85 or the control means I25 may be modified to limit to substantially more than z'ero the minimum proportion of the cycle during which the contacts '92 or I22 are closed, also in respect of any such limitation the maximum or minimum may be provided at whatever percentage may be preferred. I

Further it will be apparent that various other changes and modifications may be made, within the purview of my inventi-om and accordingly it will and is to be understood that the foregoing disclosure is illustrative only, and that my invention is not limited thereto.

Wherefore I claim:

1. Switch mechanism for controlling an electric heating unit, comprising a plurality of switch contactmembers in the circuit to said unit and arranged to complete or disrupt said circuit, at least two of said contact members being mounted for individual and relative movement, biasedto switch open position, and movable to switch closed position, and a, fixed contact member positioned for coaction with one of said movable contact members and electrically connected to the other movable contact member, and actuating means operable to cyclically move said movable contact members into circuit completing contact and permit separation movement of said movable contact members into circuit disrupting position, and a variable positioning device coacting with the movable contact members to vary the actuating efiect of the actuating means on said contact members whereby to vary the proportionate part of each actuating cycle duringwhich said contact means are in and out of circuit completing engagement, said variable positioning device being further effective to completely remove the normally spaced movable contact members from the actuating influence of the cyclic actuating means and maintain said movable contact members in circuit open position, and said variable positioning device being still further effective to completely remove the normally spaced movable contact members from the actuating influence of the cyclic actuating means and to move the movable contact member other than that contact member connected to the fixed contact member into circuit completing contact with said fixed contact member.

2. Switch mechanism for controlling an electric heating unit, comprising a plurality of switch contact members in the circuit to said unit and arranged to complete or disrupt said circuit, at least two of said contact members being mounted for individual and relative movement, biased to switch open position, and movable to switch closed position, and a fixed contact member positioned for coaction with one of said movable contact members and electrically connected to the other movable contact member, and actuating means including a cam operable to cyclically move said'movable contact and permit separation movement of said movable contact members into circuit disrupting position, and a variable positioning device coacting with the movable contact members to vary the spacing between said contact members relative to the effective surface of the actuating cam whereby to vary the proportionate part of each actuating cycle during which said contact means are in and out of circuit completing engagement, said variable positioning device being further efiective to completely remove the normally spaced movable contact members from 11 the actuating influence of the cyclic actuating means and maintain said movable contact members in circuit open position, and said variable positioning device being still further efiective to completely remove the normally spaced movable contact members from the actuating influence of the cyclic actuating means and to move the movable contact member other than that contact member connected to the fixed contact member into circuit completing contact with said fixed contact member.

3. Switch mechanism for controlling an electric heating unit, comprising a plurality of switch contact members in the circuit to said unit and arranged to complete or disrupt said circuit, at least two of said contact members being mounted for individual and relative movement, biased to switch open position, and movable to switch closed position, and a fixed contact member positioned for coaction with one of said movable contact members and electrically connected to the other movable contact member, and actuating means operable to cyclically move said movable contact members into cir cuit completing contact and permit separation movement of said movable contact members into circuit disrupting position, and a variable positioning device including movable cam surfaces coacting with the movable contact members to vary the effect of the actuating means on said contact members whereby to vary the propor-' tionate part of each actuating cycle during which said contact means are in and out of circuit completing engagement, said variable positioning device being further effective to completely remove the normally spaced movable contact members from the actuating influence of the cyclic actuating means and maintain said movable contact members in circuit open position, and said variable positioning device being still further effective to completely remove the normally space movable contact members from the actuating influence of the cyclic actuating means and to move the movable contact member other than that contact member connected to the fixed contact member into circuit completing contact with said fixed contact member.

4. Switch mechanism for controlling an electrict heating unit, comprising a plurality of switch contact members in the circuit to said unit and arranged to complete or disrupt said circuit, at least two of said contact members 12 being mounted for individual and relative movement, biased to switch open position, and movable to switch closed position, and a fixed contact member positioned for coaction with one of said movable contact members and electrically connected to the other movable contact member, and actuating means including a cam operable to cyclically move said movable contact members into circuit completing contact and permit separation movement of said movable contact members into circuit disrupting position, and a variable positioning device including movable cam surfaces coacting with the movable contact members to vary the spacing between said contact members relative to ,the efiective surface of the actuating cam whereby to vary the proportionate part of each actuating cycle during which said contact means are in and out of circuit completing engagement, said variable positioning device being further eiiective to completely remove the normally spaced movable contact members from the actuating influence of the cyclic actuating means and maintain said movable contact members in circuit open position, and said variable positioning device being still further effective to completely remove the normally spaced movable contact members from the actuating influence of the cyclic actuating means and to move the movable contact member other than that contact member connected to the fixed contact member into circuit completing contact with said fixed contact member.

HADLEY F. FREEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 414,714 Leonard Nov. 12, 1889 2,194,587 Brown et al. Mar. 26, 1940 2,275,918 Newell Mar. 10, 1942 2,294,573 Potter Sept. 1, 1942 2,329,417 Pearce Sept. 14, 1943 2,394,399 Newell Feb. 5, 1946 2,503,082 Tuttle Apr. 4, 1950 FOREIGN PATENTS Number Country Date 516,349 Great Britain Jan. 1, 1940 

